1. Field of the Invention
The present invention relates to a hub for bicycle, and more particularly to a protection structure for outer shell of a hub.
2. Description of the Prior Art
The conventional bicycle hubs for connecting the spokes and wheel are provided at one end with an outer shell thereof. A sprocket can be mounted onto the end of the hub. Most of the outer shells sold on the market are made of aluminum alloy in order to reduce the weight of the outer shell. However, aluminum alloy is a kind of soft metal while the sprocket is made of hard metal steel for the sake of structural rigidity.
To make it easy and quick for the splines made of aluminum alloy to be engaged with the receiving hole of the sprocket made of steel, it requires a tolerance when assembling the outer shell with the sprocket. However, the tolerance will cause a few impacts of hitting to the sprocket and the outer shell of the hub when the sprocket drives the hub to rotate. As what is mentioned, the sprocket is made of hard metal while the outer shell of the hub is made of soft metal. After the sprocket drove and collided with the outer shell for a long time, the splines on the outer peripheral surface of the outer shell would be damaged and worn down easily, reducing the engagement tightness of the splines.
A solution to the above problem is to replace the outer shell of the hub. However, replacing the outer shell will cause other problems. For example, the high price of the raw material such as aluminum is increasing rapidly, resulting in a problem of high cost. Therefore, the first impact of replacing the damaged aluminum outer shell is the increased cost.
On the other hand, there are two methods to assemble the sprocket and the outer shell of the hub. The first method is to screw the outer shell to the hub, as mentioned above, so that the outer shell can be replaced separately. The second method is that the outer shell is integrally formed on the hub, leading to a result that the outer shell must be replaced together with the hub. Thus, the second method costs more expanses on the raw material than the first method indirectly.
Therefore, the present invention has arisen to mitigate and/or obviate the afore-described disadvantages.